1. Field of the Invention
This invention relates generally to the dispersing of liquids into fluidized solids. More specifically this invention relates to a method and apparatus for atomizing liquid into fine droplets and dispersing the droplets into a suspension of fluidized solids. A specific aspect of this invention relates to the contacting of fluidized catalyst particles with a liquid hydrocarbon wherein the liquid hydrocarbon is atomized into a dispersion of fine droplets to improve the contact between the hydrocarbon and catalyst.
2. Description of the Prior Art
It has been a long recognized objective in the dispersal of fluid streams into fluid particle suspensions to deliver the liquid in small droplets. The small droplets increase interaction between the liquid and solid. Catalytic conversion of hydrocarbon streams using a fluidized stream of solid catalyst particles poses a typical example where small droplets are needed. Preferably, in hydrocarbon conversion droplet sizes become small enough to permit vaporization of the liquid before it contacts the solids.
It is well known that agitation or shearing can atomize a liquid hydrocarbon feed into fine droplets which are then directed at the fluidized solid particles. A variety of methods are known for shearing such liquid streams into fine droplets.
U.S. Pat. No. 3,071,540 discloses a feed injection apparatus for a fluid catalytic cracking unit wherein a high velocity stream of gas, in this case steam, converges around the stream of oil upstream of an orifice through which the mixture of steam and oil is discharged. Initial impact of the steam with the oil stream and subsequent discharge through the orifice atomizes the liquid oil into a dispersion of fine droplets which contact a stream of coaxially flowing catalyst particles.
U.S. Pat. No. 4,434,049 issued to Dean et al. shows a device for injecting a fine dispersion of oil droplets into a fluidized catalyst stream wherein the oil is first discharged through an orifice onto an impact member located within a mixing tube. The mixing tube delivers a cross flow of steam which simultaneously contacts the liquid. Combined flow of oil and steam exit the conduit through an orifice which atomizes the feed into a dispersion of fine droplets and directs the dispersion into a stream of flowing catalyst particles.
The injection devices of the '540 and '049 patents rely on relatively high fluid velocities and pressure drops to achieve atomization of the oil into fine droplets. Providing this higher pressure drop burdens the design and increases the cost of equipment such as pumps and exchangers that are typically used to supply liquid and gas to the feed injection device. The need to replace such equipment may greatly increase the cost of retrofitting an existing liquid-solid contacting installation with such an injection apparatus.
Other methods for atomizing liquid feeds with gaseous materials are shown in U.S. Pat. Nos. 3,152,065 and 3,654,140. FIG. 2 of U.S. Pat. No. 3,654,140 issued to Griffel et al. shows an injection device that imparts a tangential velocity to an oil stream to promote its mixing with a stream of steam which is injected into the oil outside the injection device. In U.S. Pat. No. 3,152,065 an injection device adds a tangential velocity to an annular stream of oil that flows around a central conduit. Steam passing through the center conduit contacts the oil at the distal end of injector. Steam and oil then pass through an orifice which further atomizes the oil and distributes it into a dispersion of fine droplets. In these devices, the tangential velocity of oil in combination with the expansion of the steam is relied on to provide the energy for atomizing the oil.
Although not a mixing device per se, U.S. Pat. No. 4,097,243 issued to Bartholic shows a feed distributor for FCC units that divides the hydrocarbon feed stream into a number of smaller feed streams. Dividing the hydrocarbon feed into a number of smaller streams promotes better mixing between the catalyst and the feed.
U.S. Pat. No. 4,562,046 issued to Hays et al. shows a feed injection apparatus that can subject at least a portion of the feed to several stages of mixing. The apparatus of Hays also divides the mixed feed into a plurality of different streams before it is discharged into contact with FCC catalyst.